FIG. 1 illustrates a hydraulic machine 2 of the gerotor type, found in the prior art. A shaft (not shown) engages splines 9, and rotates rotor 6. The machine 2 can operate either as a pump or motor, but since operation as a pump is perhaps easier to understand, the explanation will be framed in terms of a pump. Plates such as plate 18 in FIG. 7 seal the chambers 3 and 12 in FIG. 2, which are described below.
In FIG. 2, rotor 6 rotates about center CA, as indicated by the arrow pointing to that center. Rotor R rotates about center CB, as indicated by the arrow. The distance between centers CA and CB is defined as the "eccentricity" of the two rotors.
FIGS. 3-6 illustrate these two rotations. FIG. 3 illustrates the starting position. Dots D1 and D2 have been added for reference. In FIG. 4, rotor 6 has been rotated counter-clockwise by the shaft (not shown) through about 20 degrees. The other rotor R is carried along, but not through a full 20 degrees (because the tooth ratio between the rotors is 6/7). Chamber CH1 has been reduced in volume, thereby causing fluid to become expelled through conduits which are not shown.
In FIG. 5, rotor 6 has been further rotated another 20 degrees counter-clockwise. Rotor R is again carried along, but not the full 20 degrees, and chamber CH1 is further reduced in volume.
In FIG. 6, rotor 6 has been further rotated another 20 degrees, for a total of 60 degrees, compared with FIG. 3. Rotor R is carried along, but, again, not by the full 20 degrees. Now a visible separation SEP between dots D1 and D2 begins to appear, indicating the lag of rotor R behind rotor 6. Chamber CH1 is almost compressed to zero volume.
When the machine operates as a motor, the opposite sequence occurs: pressurized fluid delivered to chambers such as CH1 forces the chambers to expand, thereby inducing rotation of both rotors 6 and R about their respective centers CA and CB.